Buoys fitted with cartoon-like eyes act a little like scarecrows, keeping seabirds safely away from areas of the sea where they might get caught in fishing nets.
An estimated 400,000 diving birds drown each year when they become entangled in vertically orientated gillnets that hang down in water between floats or buoys.
In a bid to reduce the death toll, a team of bird conservation researchers led by Yann Rouxel at the BirdLife International Marine Programme in Glasgow, UK, has developed and tested a method of turning the buoys into marine scarecrows.
Researchers previously hoped LED lighting would alert seabirds to the nearly transparent nets, but the birds got tangled up and drowned anyway, says Rouxel. Then his team noticed that digital, moving eyes on the screens surrounding airport runways successfully keep birds away from planes. They decided to adapt the concept for use by fishing industry, with a device that needs no electricity to run, and is both lightweight and inexpensive.
Based on previous studies about seabird vision and what changes their flight patterns and brain activity, the researchers created a Looming-Eyes Buoy (LEB) prototype out of carbon and steel. It features a panel that rotates in the wind a bit like a weather vane. On one side of the panel the researchers added a small pair of eyes; on the opposite side they added a larger pair of eyes, so that as the device spins it gives the impression of a strange creature that is appearing, or looming, in the field of vision.
“The wind changes a lot, so that creates a looming eye movement that is hard to predict and could keep the birds from habituating [getting used to the threat] too quickly,” says Rouxel.
This sort of looming phenomenon has been shown to trigger “collision neurons” in bird brains to prevent them from running into objects or each other, he says.
The researchers adapted the size and contrast of the cartoon eyes to be detectable by Canada Geese (Branta canadensis), which have among the worst eyesight of all seabirds. They used eye-to-pupil ratios that had been shown to increase muscular tension – a possible sign of awareness of danger in chickens in a previous study and they added white crescent marks on the pupils to give them a more realistic 3D effect.
The team then attached the eyes to buoys to aluminium poles, and set them 100 metres apart in Estonia’s Küdema Bay, which has a large population of overwintering long-tailed ducks (Clangula hyemalis). They counted birds for four hours a day, before and after placing the LEBs during the 62-day study period.
They found that the number of long-tailed ducks dropped by up to 25 per cent within a 50-metre radius of each LEB. The effect was relatively long-lasting: it was only after two or three weeks that the birds began to swim closer to the buoys, says Rouxel. And seasonal changes or other influences may have explained that as well, he says.
Even so, gillnets usually only stay in a given place for a few days at a time, so it is less likely the birds would get used to the buoys in a real fishing scenario, says Rouxel.
Journal reference: Royal Society Open Science, DOI: 10.1098/rsos.210225
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